From the Manufacturer:
Beta sitosterol actually inhibits intestinal absorption of cholesterol by competing for the limited space for cholesterol in mixed micelles. I know, that's a stupid word to use with lay people! A "micelle" is a submicroscopic structural unit of protoplasm, composed of a cluster of molecules. Aren't you glad I shared that one?!
Anyway, beta sitosterol seems to reduce cholesterol absorption in the intestine by about 50%. It may have additive effects with herbs and supplements that also lower cholesterol levels. Some of these supplements include chromium, flaxseed, garlic, gaur gum, niacin, oat bran, psyllium, and others!
There's also some preliminary evidence that beta sitosterol might also have anticancer and immune stimulant effects.